Weft-detecting method and apparatus



Nov. 7, 1967 1.. J. SMITH 3,350,933

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INVENTOR.

LEO 3'. SMITH M, M 2 W Nov. 7, 1967 J. SMITH 3,350,933

WEFT-DETECTING METHOD AND APPARATUS Filed June 29, 1965 2 Sheets-Sheet 2 TRANSDUCER A 72 (SUN!) FIG. 7 Bow 1% (Diff.) B o TRANSDUCER B3 W 68 P fi-miff.

INVENTOR. LEO I SMITH 3,350,933 WEFT-DE'IECTING METHOD AND APPARATUS Leo J. Smith, Cornelius, N.C., assignor to Mount Hope Machine Company, Incorporated, Taunton, Mass., a corporation of Massachusetts Filed June 29, 1965, Ser. No. 468,083 12 Claims. (Cl. 73-159) This invention relates to an improved method and apparatus for detecting the angular relationship of weft or lateral elements to warp or longitudinal elements of a travelling web or sheet.

Reference is made to the copending application of Robert O. Gibb, Ser. No. 429,192, filed Jan. 12, 1965, and entitled, Weft-Detecting Method and Apparatus, which is a continuation-in part of application Ser. No. 253,551, filed Jan. 24, 1963, now abandoned. That application describes and claims a weft-detecting method and apparatus which employ lateral stretching of the web, in its plane of travel, to induce a distortion pattern which reflects the relationship between the weft and warp elements. The tension applied transversely to the web stretches the weft elements and causes the warp elements to assume lateral curvatures; the slopes of these curves relative to the general direction of web movement, measured on the axis of applied tension, indicate the angular relationship between the warp and weft elements. This method, however, requires both a means for stretching the web laterally along a tensioning axis, and a separate means for tracking and detecting the slope of the warp elements at that axis.

I have now discovered that the angular relation between that weft and warp of a web, travelling longitudinally under tension in a normal process of manufacture or treatment, can be detected without the use of separate means for stretching the web transversely. It is the primary object of my invention to provide an improved method and apparatus for detecting the angular relationship between the weft and warp elements of a travelling web; and to detect this relationship by a simplified procedure without sacrificing accuracy or responsiveness to varying conditions. Further objects and advantages of the invention will become apparent as the following description proceeds.

According to my new method, I depress a member into the web normal to its surface, to distort the web into a local three-dimensional distortion; and detect the direction, in a plane parallel to the web surface, of movement of warp elements passing directly under the depressing element. Preferably, the depressing is performed by a member which also tracks or senses the local direction of movement of the warp elements which it engages, since this facilitates detection of that direction. A caster wheel is well suited for this purpose.

The depression of a local region of the web stretches the warp and weft elements in the immediate vicinity into curves whose projections on the undistorted plane of the web are convex toward the depressing member; but the warp and weft elements directly engaged by the depressing member are affected in a different fashion. If the warp and weft elements are in normal perpendicular relationship, the projections of the curves of the warp elements directly engaged by the depressing member remain rectilinear, and these warp elements continue to travel in the direction of movement of the web as a whole. However, if there is a non-perpendicular relationship or skewed condition, the warp elements directly engaged by the depressing member assume a direction of travel at an angle to the overall direction of cloth movement.

The sense of this angular relationship depends upon the sense of the local skew, i.e. whether the weft elements United States Patent 3,350,933 Patented Nov. 7, 1967 are leading to the right or to the left of the depressing member. By detecting this local direction of warp movement, the relation of the weft elements can therefore be determined readily. The cause of this phenomenon appears to be that since the points of intersection or connection between the warp and weft elements remain the same; and since the existence of a skewed condition causes the peaks of the curves in warp elements on one side of the depressing member to fall upstream or downstream relative to the peaks of the curves in warp elements on the other side; the warp elements directly engaged by the depressing member must travel at an angle to continue to be equally spaced from the adjacent differently-curved warp elements.

The angular direction of movement of the depressed warp elements generally differs only slightly from the overall direction of movement of the web, depending somewhat upon the depth to which the web is depressed; therefore, it is desirable to use sensitive means for detecting this angular direction. In preferred embodiments, I depress the web by means of a caster wheel, and use electric eye apparatus for determining the angular deviation. However, other transducer means of appropriate sensitivity may also be used to sense this deviation.

Any number of depressing members may be applied to different local regions of the web, to determine abnormalities in as many places as may be desired. Detection of the weft condition in at least two locations spaced across the centerline of the web permits discrimination between the characteristic bow and skew elements of a compound abnormality. If the weft elements are bowed from end to end, the slopes of the tracked warp elements in regions on opposite sides of the centerline will be of opposite senses with respect to the direction of web travel; whereas a skew abnormality is reflected by angular deviations of the same sense in each of these regions. In a manner similar to that described in the aforementioned patent application Ser. No. 429,192, the signals of two or more detectors may be combined to provide separate output signals independently indicative of bow and skew distortions. A compound distortion is a combination of these two characteristic types, which are corrected independently, according to these separate output signals. The output signals are produced by algebraically adding and subtracting the detector signals simultaneously; the additive output signal indicates skew abnormality, and the subtractive output signal indicates how abnormality. These signals may be applied in a well-known manner to control conventional mechanisms for correcting any particular abnormality which arises.

While the specification concludes with claims particularly pointing out the subject matter which I regard as my invention, it is believed that a clearer understanding inay be gained from the following detailed description of preferred embodiments, referring to the accompanying drawings, in which;

FIG. 1 is a diagrammatic representation of a travelling woven web in which the weft elements are skewed, with their ends at the right-hand edge of the web leading their ends at the left-hand edge; and showing a distortion pattern produced according to the new method of detection; FIG. 2 is a view similar to FIG. 1, but showing the distortion pattern produced when the weft elements are in proper right-angular relationship to the warp elements; FIG. 3 is a view similar to FIG. 1, but showing the effect produced when the weft elements are skewed with their left-hand ends leading their ends at the right-hand edge;

FIG. 4 is a diagrammatic representation showing means for detecting a bow distortion, which is made up essentially of a skew distortion at the left-hand edge region similar to that of FIG. 1, and a skew distortion at the right-hand edge region similar to that of FIG. 3;

FIG. 5 is a sectional view in elevation of a preferred form of detector apparatus according to the invention;

FIG. 6 is a sectional view taken along line 66 in FIG. 5, looking in the direction of the arrows;

FIG. 7 is a wiring diagram showing the coupling of the transducers of two detectors to provide output signals separately indicating both how and skew distortions; and

FIGS. 8 and 9 are diagrams showing the relative phases and magnitudes of the transducer signals in the circuit of FIG. 7, and the output signals which are produced when the weft elements are skewed and bowed, respectively.

Referring to FIGS. l-6, a travelling woven web 10 comprises warp elements 12 extending in a direction of longitudinal web movement indicated by the arrow, and transverse weft elements 14.

In FIGS. 4 and 5, the web 10 is shown passing over guide rolls 16, 18, which form a portion of apparatus winding the web in the direction shown by the arrow, and holding it under longitudinal tension, as is common in web manufacturing and treatment processes. FIGS. 1 and 3 show small portions of a web surface having a pure skew distortion, while FIG. 2 shows a similar portion with the warp and weft elements in a normal perpendicular relationship. In FIG. 4, a condition of pure bow is suggested, in which the weft elements are curved from edge to edge of the web, with their central portions leading in the illustrated case. It will be understood that normally-occurring distortions may be compounded of both skew and bow components. It will also be observed that the bowed condition shown in FIG. 4 corresponds to oppositely-skewed conditions of the portions of the web lying on opposite sides of the centerline; thus FIGS. 1 and 3 may alternatively be regarded, for purposes of illustration, as representing regions at the left and right of the web of FIG. 4.

According to the method of the present invention, a member 20 is depressed in a normal direction into the surface of the web, to produce a local distortion pattern such as is represented in FIGS. 1-3. The direction of travel of longitudinal warp elements directly engaged by this member, relative to the overall longitudinal direction of travel of the web, is tracked or sensed, and is a measure of the angular relationship between the warp and weft elements passing that region. According to a preferred practice, the depressing and tracking functions are conveniently performed in common by a member 20 comprising a swivelling caster wheel, whose depression of the web from its plane of normal travel is shown in FIG. 5. The optimum range of the depth of this depression can be determined experimentally, and may vary with the type of web, the longitudinal tension, the sensitivity of detection, and other factors. It should not be so great that the caster wheel is constrained to ride at all times parallel to the diretcion of web travel, by vertically stretching adjacent portions of the web so that they constrain the wheel laterally; but should on the other hand be great enough to produce a substantial distortion pattern, for otherwise the degree of angular displacement of the wheel may be too small for accurate measurement by transducers of available sensitivity.

The weft elements 14 and warp elements 12 are stretched into three-dimensional curves by the depression of the web, and the projections of all these curves on the plane of web travel are convex toward the caster wheel 20. However, elements directly contacted by the caster wheel, which are illustrated as a single warp element 22 and weft element 24, are not curved in this fashion. Because the points of connection between the warp and weft elements remain stable, the contacted elements 22 and 24 are equally spaced between the adjacent oppositelycurved elements, and follow an avei age path between the two. Thus, in the normal perpendicular relationship of the elements of the web shown in FIG. 2, the projections of the elements 22 and 24 on the plane of web travel appear as straight lines. The caster wheel 20 is then aligned with the indicated direction of travel.

However, if a skew condition is present, as in FIGS. 1 or 3, the contacted warp element 22 assumes a slight transverse curvature and passes under the caster wheel at an angle to the direction of web movement. The magnitude and direction of this angle depends upon the degree and sense of the skew condition, and therefore is a measure of the skew abnormality. To explain this phenomenon, it may be noted that the greatest transverse tension applied by the caster wheel occurs in the weft element 24 which it directly engages, so that the peaks of the curvatures of the warp elements to the right or left occur along this particular weft element. Since in FIG. 1 there is a skew leading at the right edge, the peaks of the warp curves to the right of the caster wheel are slightly downstream of the peaks of the curves of warp elements to the left. Since the points of connection between the warp and weft elements remain the same, the engaged warp element 22 must remain equally spaced between the two adjacent non-engaged warp elements; and must therefore be pulled to the right upstream of the caster wheel, and slightly to the left downstream. A curvature is thus induced in the engaged warp element whose slope relative to the direction of web travel, measured under the caster wheel, reflects the skew condition. It will be understood that the converse situation exists in FIG. 3, where the skew leads at the left edge, and the curve of the warp element 22 is sloped to the right.

Referring to FIG. 4, it will be observed that two depressing members or caster wheels 20 are spaced equally on opposite sides of the centerline of the Web. In the bowed condition partially indicated by cross-hatching, the condition of the left-hand portion of the web is similar to that of FIG. 1, while the condition at the right side is similar to FIG. 3. If a pure skew existed, with the weft elements being straight but leading at the left or right, both caster wheels would be inclined in the same angular sense from the direction of the web movement. When a bow distortion appears, however, the wheels are turned oppositely relative to the direction of web travel. In a manner to be described hereinafter, the measured angular positions of both caster wheels may be combined in a manner to discriminate between components of bow and skew distortion, which commonly occur together in a compound abnormality. Additional caster wheels may be applied at any point on the web surface to determine local conditions, as desired.

A transducer is provided to detect and signal the angular position of each caster wheel 20, and these elements are incorporated in a detector assembly, of which a preferred embodiment is shown in FIGS. 5 and 6. A mounting arm 30 is provided to support the assembly with the wheel 20 depressed to a selected degree into the web, by means of transverse supports or the like (not shown). Provision for varying the depth of depression, and for lateral and longitudinal re-location, may be made if desired. A base casting 32 is attached to the mounting arm by means of screws 34, and has a cover 36 to protect the interior parts. Electrical connections are made by leads 37 through the arm 30, and thence through an opening 38 and holes 40 in the base casting.

The caster wheel 20 is supported rotatably on an arm 42, which is pivotally mounted in the base casting by means of a shaft 44, attached to the arm by a Woodrufr' key 46. The shaft 44 is supported rotatably in bearing units 48, which are in turn mounted in an annular bearing housing 50. The caster wheel is thus free to swivel about an axis normal to the plane of travel of the web.

At the upper end of the shaft 44, a shutter 52 is carried by an arm 54, received in transverse openings through the shaft and shutter, and secured in an adjusted relation by means of set screws 56. The shutter block partially obscures each of a pair of photocells 58 transversely spaced in the base casting 32, and having suitable connecting leads 37 passing through the openings 40 and 38 to external means (not shown) for indicating the weft condition, and/ or controlling it. A lamp 60 is mounted in the bracket 62 within the cover 36, and distributes light of variable intensity between the two photocells, depending upon the angular position of the shutter block and the connected caster wheel 20. In the neutral position shown, with the wheel aligned with the direction of web travel, the shutter obscures each photocell equally; but if the wheel turns in either angular direction, an unbalanced condition results. The ph-otocells are connected in a bridge circuit (FIG. 7) in a conventional manner, so that a signal is produced whose magnitude reflects angular dis placement of the caster wheel, and whose phase reflects the sense of the displacement.

A transducer of the photoelectric type is particularly sensitive to slight variations in the caster wheel angle, and is therefore well adapted to this application. However, other transducer means for detecting the angle of the caster wheel, or other tracking element, and converting the measurement to a usable output signal, may also be utilized. For example, a variable inductance device, such as is illustrated in the aforementioned patent application Ser. No. 429,192 may be used, if it is made sufficiently sensitive. As previously indicated with reference to FIG. 4, the signals of two or more detector units may be combined in a manner concurrently to produce output signals indicating separately the skew and bow components of any compound distortion. This is particularly useful in the control of weft straightening devices which employ different means for correcting bow and skew components of distortion.

The production of concurrent signals may be performed by a circuit as shown in FIG. 7, in which the output signals of the transducers A, B of two detector assemblies are algebraically added and subtracted simultaneously. The output coils 68 of the transducers form the primaries of transformers each having a pair of equivalent secondary windings 70 and 72. The pair of windings 70 is connected in series-aiding relation, and provides an output voltage which represents an algebraic addition of the inputs from the individual transducers, i.e., a skew signal. The pair of windings 72 are connected in series-opposing relation, and afford an output voltage which represents the algebraic difference between the transducer inputs, i.e., a bow signal.

Examples of the process of addition and subtraction of the transducer voltages are graphically illustrated in FIGS. 8 and 9. First assuming a normal perpendicular relationship of the warp and weft elements of the web, the transducers produce no output signal. Signals indicating a skewed condition are illustrated in FIG. 8, such as are produced when the caster wheels of two detector units are displaced in the same angular sense; these signal voltages are in phase with one another. Therefore, their summation provides a positive measurement of the degree of a skew condition, whose sense is indicated by the phase of the output signal. In the case of apure skew abnormally without bow, and assuming that the detectors are spaced substantially equally from the adjacent selvages of the web, the magnitudes of the two transducer signals are substantially equal and no subtractive or low signal is produced.

In the case of a bowed condition, as illustrated in FIG. 9, the two transducer signals are of substantially equal magnitude, but the opposite directions of angular displacement of the two caster wheels cause these signals to be relatively reversed in phase. Therefore, a summation of the signals produces a null skew signal, but the algebraic subtraction provides a signal whose amplitude measures the degree of a bow abnormality, and whose phase indicates the sense of the bow, i.e. whether the edges of the Weft elements are leading or trailing their centers.

It will be understood by those skilled in the art that various changes and modifications may be made in the illustrated embodiments without departing from the true spirit and scope of the invention. For example, separate means may be used for depressing the web and for tracking or sensing the resulting angle of travel of the engaged warp elements. I therefore intend to define the invention in the appended claims without limitations to the details of the illustrated embodiments.

What I claim is:

1. The method of detecting the angular relationship between transverse and longitudinal elements of a web travelling under longitudinal tension, which comprises the steps of: depressing a member into a region of the web normal to its surface to produce a local distortion pattern, and detecting the direction of travel of longitudinal elements of the web engaged by said member, relative to the longitudinal direction of travel of the web, as a measure of the undistorted relationship between transverse and longitudinal elements passing through said region.

2. The method of detecting the angular relationship between transverse and longitudinal elements of a web travelling longitudinally under tension, by means of a depressing member capable of tracking and sensing the local direction of movement of longitudinal elements engaged thereby, which comprises the steps of: depressing said member into the web to stretch the web normal to its surface and thereby locally distort a region of the web adjacent to said member, whereby longitudinal elements directly engaged by said member and whose local direction of movement is tracked by said member, travel in a direction determined by the angular relation between the transverse and longitudinal elements when undistorted; and detecting the direction of movement tracked by said member, as a measure of the undistorted relationship between the transverse and longitudinal elements passing through said region.

3. The method of detecting the angular relationship between transverse and longitudinal elements of a web travelling under longitudinal tension, by means of a rotatable detector wheel supported for swivelling to track the direction of travel of relatively-moving elements engaged thereby, which method comprises the steps off: depressing the detector Wheel into a region of the web normal to its surface to produce a local distortion pattern, and detecting the angular relation assumed by the detector wheel relative to the longitudinal direction of travel of the web, as a measure of the undistorted relationship between transverse and longitudinal web elements passing through said region.

4. The method of detecting the angular relationship between transverse and longitudinal elements of a Web, which comprises the steps of: feeding the web in a longitudinal direction under tension, depressing a region of the web normal to its surface to produce a local distortion pattern, and detecting, in the depressed region, the angular relation of longitudinal elements of the web to the overall-direction of travel of the web, as a measure of the undistorted relationship between transverse and longitudinal web elements passing through said region.

5. The method of simultaneously detecting bow and skew components of an abnormal non-perpendicular relationship between transverse and longitudinal elements of a web travelling under longitudinal tension, which method comprises the steps of:

depressing members into the web at two locations equally spaced on opposite sides of the centerline thereof, to stretch the web normal to its surface and thereby locally distort regions of said web adjacent to said members, whereby longitudinal elements directly engaged by said members travel under said members in directions determined by the angular relation between the transverse and longitudinal elements when undistorted;

independently detecting the angles under said members between the directions of said engaged elements and the direction of web travel; and simultaneously adding and subtracting the algebraic values of the detected angles to produce independent measures of skew and bow abnormalities in the relationship between the transverse and longitudinal elements.

6. The method of simultaneously detecting bow and skew components of an abnormal non-perpendicular relationship between transverse and longitudinal elements of a web travelling under longitudinal tension, by means of a pair of members each constructed and arranged to track a local direction of movement of longitudinal elements engaged thereby, and a pair of transducers each constructed and arranged to produce a signal responsive to the direction of tracking of one of said sensing members, which method comprises the steps of:

depressing the tracking members into the web at two locations equally spaced on opposite sides of the centerline thereof, to stretch the web normal to its surface and thereby locally distort regions of said web adjacent to said members, whereby longitudinal elements directly engaged by said members and whose local direction of movement is tracked by said members, travel in directions determined by the angular relation between the transverse and longi tudinal elements when undistorted;

independently detecting the angles between said local directions of movement and the direction of web travel, tracked by each of said members;

and simultaneously adding and subtracting the signals of said transducers to produce independent measures of skew and bow abnormalities in the relationship between the transverse and longitudinal elements.

7. Apparatus for detecting the angular relationship between transverse and longitudinal elements of a web travelling under longitudinal tension, comprising a depressing member, means for depressing said member into a region of the web normal to its surface to produce a local distortion pattern, and means constructed and arranged for detecting the direction of travel of longitudinal elements of the web engaged by said member, relative to the longitudinal direction of travel of the web, as a measure of the undistorted relationship between transverse and longitudinal elements passing through said region.

8. Apparatus for detecting the angular relationship between transverse and longitudinal elements of a web travelling longitudinally under tension, comprising a depressing member constructed and arranged for angular movement to track the local direction of movement of longitudinal elements engaged thereby; means for depressing said member into the web to stretch the web normal to its surface and thereby locally distort a region of the web adjacent to said member, whereby longitudinal elements directly engaged by said member and whose local direction of movement is tracked by said member, travel in a direction determined by the angular relation between the transverse and longitudinal elements when undistorted; and means constructed and arranged for detecting the direction of movement tracked by said member, as a measure of the undistorted relationship between the transverse and longitudinal elements passing through said region.

9. Apparatus as recited in claim 8, in which said detecting means comprises a shutter member drivingly connected with said depressing member for displacement according to the angular tracking direction assumed by said depressing member, photoelectric cell means operatively related to said shutter member for variable shading thereby according to the displacement thereof, and circuit means incorporating said photoelectric cell means for producing a signal indicative of said angular tracking direction.

10. Apparatus as recited in claim 9, in which said cell means comprises a pair of photoelectric cells constructed and arranged for unequal shading by said shutter member in positions assumed thereby when the tracking direction of said depressing member is at an angle to the direction of web travel.

11. Apparatus for detecting the angular relationship between transverse and longitudinal elements of a web travelling under longitudinal tension, comprising a caster wheel; means supporting said wheel for swivelling movement to track the local direction of travel of relativelymoving elements engaged thereby, said supporting means depressing the caster wheel into a region of the web normal to its surface to produce a local distortion pattern, and means constructed and arranged for detecting the angular relation assumed by said wheel relative to the longitudinal direction of travel of the web, as a measure of the undistorted relationship between transverse and longitudinal web elements passing through said region.

12. Apparatus for simultaneously detecting bow and skew components of an abnormal non-perpendicular relationship between transverse and longitudinal elements of a web travelling under longitudinal tension, comprising: a pair of members each constructed and arranged to track a local direction of movement of longitudinal elements engaged thereby; means for depressing said tracking members into the web at two locations equally spaced on opposite sides of the centerline thereof to stretch the web normal to its surface and thereby locally distort regions of said web adjacent to said members, whereby longitudinal elements directly engaged by said members and whose local direction of movement is tracked by said members, travel in directions determined by the angular relation between the transverse and longitudinal elements when undistorted; a pair of transducers each constructed and arranged to produce a signal responsive to the angular direction of tracking of one of said sensing members, relative to the direction of web travel; and circuit means connected for simultaneously adding and substracting the algebraic values of the signals of said transducers to produce output signals independently indicating skew and bow abnormalities in the relationship between the transverse and longitudinal elements.

References Cited UNITED STATES PATENTS 2,795,029 6/1957 Robertson et al. 73-159 FOREIGN PATENTS 707,954 4/1965 Canada.

LOUIS R. PRINCE, Primary Examiner.

I. NOLTON, Assistant Examiner. 

7. APPARATUS FOR DETECTING THE ANGULR RELATIONSHIP BETWEEN TRANSVERSE AND LONGITUDINAL, ELEMENTS OF A WEB TRAVELLING UNDER LONGITUINAL TENSION, COMPRISING A DEPRESSING MEMBER, MEANS FOR DEPRESSING SAID MEMBER INTO A REGION OF THE WEB NORMAL TO ITS SURFACE TO PRODUCE A LOCAL DISTORTION PATTERN, AND MEANS CONSTRUCTED AND ARRANGED FOR DETECTING THE DIRECTION OF TRAVEL OF LONGITUDINAL ELEMENTS OF THE WEB ENGAGED BY SAID MEMBER, RELATIVE TO THE LONGITUDINAL DIRECTION OF TRAVEL OF THE WEB, AS A MEASURE OF THE UNDISTORTED RELATIONSHIP BETWEEN TRANSVERSE AND LONGITUDINAL ELEMENTS PASSING THROUGH SAID REGION. 